This invention relates generally to a power control arrangement for surface heating units in a cooking appliance such as a domestic range, and more particularly to an arrangement for controlling surface units operated in a dual mode to jointly heat a utensil such as a griddle.
Electric ranges are now commercially available providing a griddle feature. Typically, in such ranges four surface units are clustered in a generally rectangular arrangement on the cooktop. Three of the surface units are standard surface units and one is an automatic surface unit, for which power is controlled as a function of the temperature of the utensil being heated thereon. Often the automatic surface unit employs a higher wattage rated resistive heating element than the other three units. To operate the range in the griddle mode, a griddle is supported on and extends over the automatic surface unit and one of the adjacent standard surface units. In order to provide temperature control during griddle operation, the energization of both surface units utilized in the griddle mode is influenced by the utensil temperature sensed by the automatic surface unit sensor. One arrangement for such control is disclosed in commonly assigned U.S. Pat. No. 2,785,266 to Lewis et al. In that arrangement, the energization of the automatic surface unit is controlled by an electromechanical thermostatic switch which periodically opens and closes in accordance with the selected temperature and the sensed utensil temperature. Insertion of the griddle in position on the cooktop alters the energization circuit of the standard surface unit such that it is energized and de-energized simultaneously with the automatic surface unit.
While this arrangement works satisfactorily when both surface units have the same wattage rating, when different wattage units are switched on and off simultaneously, the griddle is heated unevenly. Another disadvantage of this arrangement is that if the automatic surface unit is already hot from previous usage when the griddle mode is initiated, but the standard unit is at room temperature, even if both units are the same wattage rating, the standard unit will heat up relatively slowly since the on times, which are determined by the sensed utensil temperature, will be relatively short due to the preheating of the unit. In such instances the griddle will be unevenly heated for an extended warm up time. Similarly, if the standard unit is pre-heated from prior use, and the automatic surface unit is not, the standard unit may be overdriven while the automatic surface is heating up resulting in a portion of the griddle surface being overheated.
Commonly assigned U.S. Pat. No. 4,493,980 discloses an improved power control arrangement for automatic surface units which replaces the electromechanical power control arrangement with an electronic control circuit. The improved power control circuit provides for more rapid temperature response and tighter temperature control. However, similar shortcomings to those discussed above may be experienced with this system as well when operating in a griddle mode.
A power control arrangement for a range featuring a griddle mode which rapidly brings the griddle to the desired temperature and which provides relatively even heating of the griddle by both surface units regardless of relative wattage rating and regardless of initial conditions would be highly desirable.
It is therefore an object of the present invention to provide for a cooking appliance of the type featuring at least two surface units, an automatic surface unit and a standard surface unit, one of which has a relatively higher wattage rating, a power control arrangement which automatically compensates for the wattage difference to provide even heating by both surface units, as a function of the temperature sensed by the automatic surface unit when operating in a griddle mode.
It is a further object of the present invention to provide for a cooking appliance having a griddle heated by two surface units, one of which is an automatic surface unit, which units may have the same or different wattage ratings, a power control arrangement in which the standard surface unit is overdriven when the automatic surface unit is relatively hot and the standard unit is relatively cool, and underdriven when the standard unit is relatively hot and the automatic surface unit is relatively cool to quickly bring the two units to approximately the same heating level for even heating of the griddle.